The present invention relates generally to ultrasonic testing of articles and, more particularly, to apparatus providing relief against backsplash resulting when the laminar flow water column used for transmitting the ultrasonic waves creates a cascading waterfall after striking the article being tested and impairs the quality of the water column.
II. Description of the Prior Art
It has long been known to perform nondestructive inspection employing ultrasonic waves travelling between a transducer and the article being inspected. Since liquids are a good media for transmitting this wave energy, it has been customary in the past to submerge the transducer or transducers and the object to be inspected, or at least part of the object to be inspected, in the liquid medium. This system worked as long as the object being inspected was not too large. However, it was completely impractical when the object being inspected was of substantial size such as, for example, large sheets or plates.
For such large objects, it heretofore became the practice to mount the transducer in a suitably shaped container which had an opening shaped to closely match the contour of the object and, by keeping the container filled with liquid, to attempt to maintain a fluid seal sufficient to keep the container full and a liquid coupling between the transducer and the object. This method had the inherent disadvantage of requiring a close fit between the edges of the container and the surface of the object being inspected which made it impossible to accommodate large surface defects and protrusions such as weld beads, gouges, or changes in contour, without losing the liquid coupling. Since a break in the fluid connection between the transducer and the article interrupts the inspection process, this method proved to be unsatisfactory.
Another method sometimes suggested for coupling the transducer to the article employs a housing for the transducer which has an outlet equipped with a nozzle. The liquid is introduced into the housing under pressure so that it is expelled through the nozzle toward the surface of the object as a high velocity, uncontained, stream or jet of liquid. The transducer is located in the housing so that the ultrasonic waves can travel to the article through this high velocity stream of liquid. In more recent versions of this method, a pair of aligned transducers with their associated nozzles are positioned on opposite sides of a large plate or other object to be inspected. This has generally come to be a very satisfactory ultrasonic inspection method.
In order to more clearly define the evolution of ultrasonic inspection techniques and the existing state of the art in this regard, a number of specific prior art disclosures will here be mentioned. For example, U.S. Pat. Nos. 3,662,590 issued May 16, 1971 to Shiraiwa, No. 3,555,891 issued Jan. 19, 1971 to Lewis, and No. 3,255,626 issued Jun. 14, 1966 to Van Der Veer all broadly disclose ultrasonic inspection apparatus. U.S. Pat. No. 3,121,325 issued Feb. 18, 1964 to Rankin et al. discloses the use of air jets from a manifold to keep the top surfaces of ultrasonic probes free of the coupling water. U.S. Pat. Nos. 3,122,661 issued Feb. 25, 1964 to Joy and 3,420,097 issued Jan. 7, 1969 to Battermann et al., disclose the use of air jets in combination with ultrasonic inspection devices to confine the coupling fluid to a desired area. U.S. Pat. No. 3,745,833 issued Jul. 17, 1973 to Armstrong and French Patent No. 1,275,693 issued Nov. 2,1961 to U.K Atomic Energy Authority both disclose the use of air jets in combination with ultrasonic inspection devices to deflect the coupling water stream. U.S. Pat. No. 2,751,783 issued Jun. 26, 1956 to Erdman and Japanese Disclosure No. 46-8391 dated Aug. 2,1967 to Mitsubishi Juko disclose, respectively, a splash box and a shield for containing the coupling water stream used in an ultrasonic inspection device.